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The rapid proliferation of holopelagic Sargassum in the tropical Atlantic Ocean presents environmental challenges and economic opportunities. In 2022, Senegal witnessed its first significant holopelagic Sargassum beaching event, triggering widespread concern and interest from civil society, industrial sectors and government. This study represents the first analysis of stranded holopelagic Sargassum's morphotypes and chemical composition in North West Africa. We highlight the distinct nature of Sargassum stranding in Senegal, dominated by S. fluitans III, and describe a novel morphotype. Compared to the tropical Atlantic, Senegalese Sargassum displayed lower arsenic concentrations, higher cadmium levels, and increased mercury content. The biochemical analysis revealed high total protein levels in Senegalese samples. Furthermore, variations in biochemical composition within various parts of the Sargassum thallus were observed. These findings offer valuable insights into potential applications and limitations. Our study identifies promising uses in Senegal and neighbouring countries, mainly for animal feed and agriculture and in the chemical industry, where notable palladium content is observed and, to a lesser extent, the phenolic compounds and mannitol. Our interdisciplinary approach enhances the global scientific understanding of the Sargassum issue and aids in developing sustainable strategies for African coastal regions grappling with climate change and invasive species. With the anticipation of more frequent Sargassum beaching events and more generally for seaweed exploitation, we advocate for inter-governmental African organisations to establish standardised norms for their exploitation. We also recommend that the Food and Agriculture Organization/World Health Organization consider incorporating more seaweed in the Codex Alimentarius.

Macroalgae (or seaweed) aquaculture can potentially provide many ecosystem services, including climate change mitigation, coastal protection, preservation of biodiversity and improvement of water quality. Nevertheless, there are still many constraints and knowledge gaps that need to be overcome, as well as potential negative impacts or scale-dependent effects that need to be considered, before macroalgae cultivation in Europe can be scaled up successfully and sustainably. To investigate these uncertainties, the Expert Working Group (EWG) on Macroalgae was established. Its role was to determine the state of knowledge regarding the potential of macroalgae culture in providing climate-related and other ecosystem services (ES) and to identify specific knowledge gaps that must be addressed before harvesting this potential. The methodological framework combined a multiple expert consultation with Delphi process and a Quick Scoping Review (QSR). To analyse the outcome of both approaches, the EWG classified the findings under the categories Political, Environmental, Social, Technical, Economic and Legal (PESTEL approach) and categorised the ES based on the CICES 5.1 classification. Although representative stakeholders from many different disciplines were contacted, the majority of responses to the Delphi process were from representatives of academia or research. While the results of each method differed in many ways, both methods identified the following top six ecosystem services provided by seaweed cultivation: i) provisioning food, ii) provisioning hydrocolloids and feed, iii) regulating water quality, iv) provisioning habitats, v) provisioning of nurseries and vi) regulating climate. Diverse technological knowledge gaps were identified by both methods at all scales of the macroalgae cultivation process, followed by economic and environmental knowledge gaps depending on the method used. Based on suggestions from the expert respondents in the Delphi process, there is a cl

Macroalgae (or seaweed) aquaculture can potentially provide many ecosystem services, including climate change mitigation, coastal protection, preservation of biodiversity and improvement of water quality. Nevertheless, there are still many constraints and knowledge gaps that need to be overcome, as well as potential negative impacts or scale-dependent effects that need to be considered, before macroalgae cultivation in Europe can be scaled up successfully and sustainably. To investigate these uncertainties, the Expert Working Group (EWG) on Macroalgae was established. Its role was to determine the state of knowledge regarding the potential of macroalgae culture in providing climate-related and other ecosystem services (ES) and to identify specific knowledge gaps that must be addressed before harvesting this potential.

The bacterial communities of Caulerpa lentillifera were studied during an outbreak of an unknown disease in a sea grape farm from Vietnam. Clear differences between healthy and diseased cases were observed at the order, genus, and Operational Taxonomic Unit (OTU) level. A richer diversity was detected in the diseased thalli of C. lentillifera, as well as the dominance of the orders Flavobacteriales (phylum Bacteroidetes) and Phycisphaerales (Planctomycetes). Aquibacter, Winogradskyella, and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. The Rhodobacteraceae and Rhodovulum dominated the bacterial community composition of healthy C. lentillifera. The likely beneficial role of Bradyrhizobium, Paracoccus, and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The bleaching of diseased C. lentillifera might not only be associated with pathogens but also with an oxidative response. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further applied and basic research is urgently needed on C. lentillifera microbiome, shotgun metagenomic, metatranscriptomic, and metabolomic studies as well as bioactivity assays are recommended.

This study describes the adoption and validation of two innovative methods for the automated count of Ostreopsis spp. concentration in sea water: a molecular assay based on qPCR and an opto-electronic device allowing to automatically acquire images from the whole sample and recognize the target algae on the basis of a machine learning algorithm. The two approaches were tested on samples coming from different locations in 5 countries along the Mediterranean Sea, collected in the framework of the cross-border EU ENPI CBCMED Project M3-HABs, and compared with the standard visual counting method. The results demonstrate the effectiveness of both automatic approaches which provide a valuable tool, mostly cost and time effective, for the establishment of large-scale and effective monitoring of Ostreopsis spp. blooms. Moreover, the two automatic methods demonstrated the ability to discriminate for the presence of a different but similar species, O. fattorussoi, for which new species-specific qPCR primers were developed